Process of removing scales from boilers



' UNITED STATES PATENT QFFICE.

JOHN DRAPER, OF BROOKLYN, NEWYORK.

PROCESS OF REMOVING SCALES FROM BOILERS.

SPECIFICATION forming part of Letters Patent No. 509,209, dated November 21, 1893.

Application filed March 1 1892- Serial No. 423,404. (No specimens.) Patented in England May 12, 1891, No. 8,115, and

- January 12, 1892.110. 607.

To all whom it may concern;

Be'it known that I,JOHN DRAPER, chemist, a citizen of the United States, residing at Thirty-eighth street, above Fifth avenue, Brooklyn, New York, but at present residing at 1 Albany Street, Kelvinside, Glasgow, in the county of Lanark, Scotland, have invented certain new and useful improvements in methods of .and means for removing and preventing scales or incrustations in steam-boilers, and for the prevention of pitting, corrosion, or oxidation of such boilers,which improvements are also applicable to the coating of iron or steel articles generally so as to protect them from oxidation, (for which I have received Letters Patent in England, No. 8,115, dated May 12, 1891, and No. 607, dated January 12, 1892;) and I do hereby declare that the followingisa full, clear, and exact description of the invention, which will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to means for removing scales or incrustations from steam boilers, and for the prevention of pitting, corrosion, or oxidation of such boilers, the invention being also applicable to the coating of iron or steel articles generally so as to protect them from oxidation, and it consists broadly in coating the surface which it is desired to protect with a thin film of oxide of mercury.

According to the method of carrying out my invention I employ metallic mercury and metallic sodium or potassium, and carbonate of sodium or potassium, which when placed in a closed vessel of iron or steel containing water, will under the action of heat and pressure deposit a thin film or coating upon the walls of such vessel, and thereby protect same from pitting, corrosion and oxidation, and will also prevent the formation of scales or incrustations thereon, while in the case of boilers or other vessels upon the walls of which scales or incrustations are already formed, the use of such materials will in a comparatively short time efiectually remove the same. Further, by placing or suspending iron or steel articles generally, in the boiler or vessel containing water into which the materialsabove mentioned have been introduced, when the boiler or vessel is heated such articles will within a comparatively short period become coated with a thin film of such a nature as to effectually resist oxidation, and so protect such articles. The quantities of the materials above named which it is necessary to use are immaterial, some excess doing no injury, and the proportions may vary within large limits and will depend upon the nature of the water employed and other circumstances, but I find that ten ounces of mercury to one ounce of sodium, with sufficient carbonate of sodium or of potassium to produce by itself alkaline reaction in the water contained in the boiler or vessel, and which being in the form of a carbonate will produce better results than the alkali produced by the decomposition of the sodium present will in most cases be ample forevery five hundredsquare feet of surface to be coated.

The mercury is first mixed with the sodium metal and a hard amalgam is formed if mixed in the proportions stated. This amalgam is introduced into the Water of the boiler, and by the time the boiler is under steam the decomposition of the sodium has liberated the mercury slowly and in extremely fine particles, which division of the mercury is necessary to secure the oxidation to form the coating. The sodium, apart from its value in holding the mercury and liberating it in fine particles, is of great value on account of the ease with which it forms caustic soda with the water of the boiler, thereby greatly assisting in the oxidation of the mercury under pressure and heat, as well as its effect upon the boiler plates, cleansing them from grease and other objectionable substances. The carbonate of soda is found necessary to supply sufficient alkali to the water, first on account of the great difficulty found in depositing upon the surface of iron or steel a coating of oxide of mercury unless the Water be slightly alkaline, and secondly it has a specific efiect in neutralizing any acidity frequently found in some boiler waters. The process in practice is therefore:-The introduction of an amalgam of mercury and sodium in the stated proportions into a boiler, the raising of the water contained in the boiler to the working pressure (which may be fifty to eighty pounds per square inch), the introduction into the water of the boiler by the feed of sufficient carbonate to cause the water to be alkaline. If the water is kept in this condition the gradual liberation of the mercury is brought about by the decomposition of the mercury-sodium amalgam and is oxidized to an oxide of mercury in contact with a carbonate and with the assistance of the caustic soda. The process being carried out as described and the boiler kept in working condition, the time required to produce the best effect, while it diifers in nearly every case according to the conditions, will be approximately not more than six months nor less than three months.

The patent of the United States No. 453,882 issued to myself and Alfred Holmgren, Henry Mount and John Barnes, describes the use of water, bichloride of mercury, mercury and sodium, under heat and pressure for the purpose of coating the internal surfaces of steam boilers to prevent incrustation. It has been found almost impossible to apply the coating or enamel to the boiler plate from that composition in boilers which have a tendency from various causes such as acid feed Waters, &c., to rusting, corrosion or wasting away of the plate. In order to successfully apply the coating it is necessary that the water be kept slightly alkaline and sufficient alkali is not produced in the process described by the previous patent cited, by the decomposition of metallic sodium to maintain the required alkalinity. It would be commercially impracticable to use sufficient metallic sodium to bring about the necessary state of alkalinity on account of the cost thereof, Moreover, in the working of the former patent it was necessary to put in the materials in two operations, to wit: (first) to dissolve the HgOl in the water of the boiler, and (second) to add the mercury and sodium to the solution thus formed. In the present case a free alkali is used, all the materials are compounded together, and the whole operation is performed at once.

Referring again to boilers liable to corrosion, the amount of free alkali necessary makes it impossible to use the mercury bi chloride of the former patent on account of the decomposition expressed in the reaction as follows:

Having fully described my invention,what I claim, and desire to secure by Letters Patent, is-

The method of treating iron or steel surfaces so as to protect them from pitting, corrosion, or oxidation, or prevent the formation of scales or incrustations thereon, or to remove the same therefrom, consisting in subjecting such surfaces to the action of water, metallic mercury and metallic sodium or potassium and carbonate of sodium or of potassium under heat and pressure, as set forth.

JOHN DRAPER.

Witnesses:

CHAS. A. ALLISON, HARRY A. MOLELLAN. 

